Transcutaneous electrical nerve stimulator with automatic detection of leg orientation and leg motion for enhanced sleep analysis, including enhanced transcutaneous electrical nerve stimulation (tens) using the same

ABSTRACT

Apparatus for providing transcutaneous electrical nerve stimulation (TENS) therapy to a user, the apparatus comprising: a housing; an application unit for providing mechanical coupling between the housing and the user&#39;s body; a stimulation unit for electrically stimulating at least one nerve of the user; a sensing unit for sensing the user&#39;s body movement and body orientation; and a reporting unit for providing the user with feedback based on the user&#39;s sensed body movement and body orientation.

REFERENCE TO PENDING PRIOR PATENT APPLICATIONS

This patent application:

(1) is a continuation-in-part of pending prior U.S. patent applicationSer. No. 14/794,588, filed Jul. 8, 2015 by NeuroMetrix, Inc. and XuanKong et al. for MEASURING THE “ON-SKIN” TIME OF A TRANSCUTANEOUSELECTRICAL NERVE STIMULATOR (TENS) DEVICE IN ORDER TO MINIMIZE SKINIRRITATION DUE TO EXCESSIVE UNINTERRUPTED WEARING OF THE SAME(Attorney's Docket No. NEURO-73), which patent application:

-   -   (A) is a continuation-in-part of pending prior U.S. patent        application Ser. No. 14/610,757, filed Jan. 30, 2015 by        NeuroMetrix, Inc. and Shai N. Gozani et al. for APPARATUS AND        METHOD FOR RELIEVING PAIN USING TRANSCUTANEOUS ELECTRICAL NERVE        STIMULATION (Attorney's Docket No. NEURO-5960 CON), which patent        application:        -   (i) is a continuation of prior U.S. patent application Ser.            No. 13/678,221, filed Nov. 15, 2012 by NeuroMetrix, Inc. and            Shai N. Gozani et al. for APPARATUS AND METHOD FOR RELIEVING            PAIN USING TRANSCUTANEOUS ELECTRICAL NERVE STIMULATION            (Attorney's Docket No. NEURO-5960), which patent application            claims benefit of:            -   (a) prior U.S. Provisional Patent Application Ser. No.                61/560,029, filed Nov. 15, 2011 by Shai N. Gozani for                SENSUS OPERATING MODEL (Attorney's Docket No. NEURO-59                PROV); and            -   (b) prior U.S. Provisional Patent Application Ser. No.                61/657,382, filed Jun. 8, 2012 by Shai N. Gozani et al.                for APPARATUS AND METHOD FOR RELIEVING PAIN USING                TRANSCUTANEOUS ELECTRICAL NERVE STIMULATION (Attorney's                Docket No. NEURO-60 PROV);    -   (B) is a continuation-in-part of pending prior U.S. patent        application Ser. No. 14/269,887, filed May 5, 2014 by        NeuroMetrix, Inc. and Thomas Ferree et al. for TRANSCUTANEOUS        ELECTRICAL NERVE STIMULATOR WITH USER GESTURE DETECTOR AND        ELECTRODE-SKIN CONTACT DETECTOR, WITH TRANSIENT MOTION DETECTOR        FOR INCREASING THE ACCURACY OF THE SAME (Attorney's Docket No.        NEURO-6667), which patent application:        -   (i) is a continuation-in-part of pending prior U.S. patent            application Ser. No. 14/230,648, filed Mar. 31, 2014 by            Neurometrix, Inc. and Shai Gozani et al. for DETECTING            CUTANEOUS ELECTRODE PEELING USING ELECTRODE-SKIN IMPEDANCE            (Attorney's Docket No. NEURO-64), which claims benefit of:            -   (a) prior U.S. Provisional Patent Application Ser. No.                61/806,481, filed Mar. 29, 2013 by Shai Gozani for                DETECTING ELECTRODE PEELING BY RELATIVE CHANGES IN                SKIN-ELECTRODE IMPEDANCE (Attorney's Docket No. NEURO-64                PROV);        -   (ii) is a continuation-in-part of pending prior U.S. patent            application Ser. No. 14/253,628, filed Apr. 15, 2014 by            Neurometrix, Inc. and Shai Gozani et al. for TRANSCUTANEOUS            ELECTRICAL NERVE STIMULATOR WITH AUTOMATIC DETECTION OF USER            SLEEP-WAKE STATE (Attorney's Docket No. NEURO-65), which            claims benefit of:            -   (a) prior U.S. Provisional Patent Application Ser. No.                61/811,864, filed Apr. 15, 2013 by Shai Gozani for                TRANSCUTANEOUS ELECTRICAL NERVE STIMULATOR WITH                AUTOMATIC DETECTION OF PATIENT SLEEP-WAKE STATE                (Attorney's Docket No. NEURO-65 PROV);        -   (iii) claims benefit of prior U.S. Provisional Patent            Application Ser. No. 61/819,159, filed May 3, 2013 by            Neurometrix, Inc. and Thomas Ferree et al. for TAP DETECTOR            WITH HIGH SENSITIVITY AND SPECIFICITY FOR A WEARABLE            TRANSCUTANEOUS ELECTRICAL NERVE STIMULATOR (Attorney's            Docket No. NEURO-66 PROV); and        -   (iv) claims benefit of prior U.S. Provisional Patent            Application Ser. No. 61/858,150, filed Jul. 25, 2013 by            Neurometrix, Inc. and Andres Aguirre et al. for MOVEMENT            REGULATED TRIP CONDITIONS IN A WEARABLE TRANSCUTANEOUS            ELECTRICAL NERVE STIMULATOR (Attorney's Docket No. NEURO-67            PROV);    -   (C) claims benefit of prior U.S. Provisional Patent Application        Ser. No. 62/021,807, filed Jul. 8, 2014 by Neurometrix, Inc. and        Xuan Kong et al. for MEASURING TENS DEVICE ON-SKIN TIME TO        PREVENT AND MINIMIZE SKIN IRRITATION (Attorney's Docket No.        NEURO-73 PROV);

(2) claims benefit of pending prior U.S. Provisional Patent ApplicationSer. No. 62/213,978, filed Sep. 3, 2015 by Neurometrix, Inc. and ThomasFerree et al. for TRANSCUTANEOUS ELECTRICAL NERVE STIMULATOR WITHAUTOMATIC DETECTION OF LEG ORIENTATION AND ROTATION FOR ENHANCED SLEEPANALYSIS (Attorney's Docket No. NEURO-77 PROV); and

(3) claims benefit of pending prior U.S. Provisional Patent ApplicationSer. No. 62/101,029, filed Jan. 8, 2015 by Neurometrix, Inc. and ShaiGozani et al. for METHOD AND APPARATUS FOR USING TRANSCUTANEOUSELECTRICAL NERVE STIMULATION TO AID SLEEP (Attorney's Docket No.NEURO-69A PROV).

The fifteen (15) above-identified patent applications are herebyincorporated herein by reference.

FIELD OF THE INVENTION

This invention relates generally to Transcutaneous Electrical NerveStimulation (TENS) devices that deliver electrical currents across theintact skin of a user via electrodes so as to provide symptomatic reliefof pain. More specifically, this invention relates to a TENS device wornduring sleep, and a method for making novel measurements that broadenand enhance sleep analysis, and includes enhanced transcutaneouselectrical nerve stimulation (TENS) using the same.

BACKGROUND OF THE INVENTION

Chronic pain due to diabetic neuropathy and other causes can interferewith sleep, which carries a host of secondary complications.Transcutaneous electrical nerve stimulation (TENS) devices provide painrelief by stimulating sensory nerves, which leads to an increase inendogenous opioids and down-regulation of pain signal transmission tothe brain. A TENS device which could be used during sleep would offerunique opportunities to provide pain relief during bedtime with the goalof improving sleep (see, for example, Barbarisi M, Pace M C, PassavantiM B, et al. Pregabalin and transcutaneous electrical nerve stimulationfor postherpetic neuralgia treatment. Clin J Pain. September 2010;26(7):567-572).

However, most TENS devices are designed to operate exclusively duringthe day (i.e., wake state) without any nighttime (i.e., sleep state)operation. This limitation is evident in the design of conventional TENSdevices, in which the electric current is delivered through wires(called leads) that are connected to electrode pads on the skin. Such adesign is not practical or safe for use during sleep because the leadsare cumbersome and may get tangled or pulled, and because the electrodepads can potentially peel off the skin (which will terminate TENStherapy) or, perhaps worse, can potentially partially peel off the skin,leading to increased current density and negative consequences for theuser (e.g., discomfort or, in extreme cases, burns).

In pending prior U.S. patent application Ser. No. 14/230,648, filed Mar.31, 2014 by NeuroMetrix, Inc. and Shai Gozani et al. for DETECTINGCUTANEOUS ELECTRODE PEELING USING ELECTRODE-SKIN IMPEDANCE (Attorney'sDocket No. NEURO-64), published as U.S. Patent Application PublicationNo. US 2014/0296934 A1 on Oct. 2, 2014, which patent application ishereby incorporated herein by reference, there is disclosed a novel TENSdevice which allows TENS therapy to be applied during nighttime (i.e.,during sleep state) as well as during the day (i.e., wake state). Thekey design elements that make this novel TENS device suitable for useduring sleep are (1) the leads are eliminated because the electrode padsare attached directly to the housing containing the TENS stimulationcircuitry, (2) the TENS housing and electrode pads are held reliably andcomfortably against the skin by an adjustable strap or band, (3) theTENS device continuously measures skin-electrode contact impedance (andrelated electrical parameters) so as to detect if the electrode padspeel (completely or partially) off the skin and the TENS device stopsdelivering current if peeling is detected, (4) therapeutic stimulationmay be scheduled in one-hour on-off blocks so as to provide pain reliefthroughout the night, and (5) the TENS device detects when the user isasleep and reduces the therapeutic stimulation level automatically so asnot to disturb sleep.

The novel TENS device disclosed in pending prior U.S. patent applicationSer. No. 14/230,648 (and published as U.S. Patent ApplicationPublication No. US 2014/0296934 A1) is designed to be located on theupper calf of the user. This is for three reasons. First, the TENSdevice needs to stimulate sensory nerve fibers in order to providewidespread pain relief through the systemic effect of an increase inendogenous opioids and down-regulation of pain signal transmission. Theupper calf area has a cluster of sensory nerve fibers that can beactivated easily with a transcutaneous electrical nerve stimulatorbecause of their proximity to the surface of the skin. Second, someforms of chronic pain (such as that due to diabetic neuropathy) areexperienced most acutely in the feet, and in addition to the mechanismof pain suppression through endogenous opioids described above (which issystemic), there is also evidence for additional mechanisms of painsuppression that are more local, thus making it advantageous to placethe TENS device on the upper calf of the user. Third, chronic pain canbe persistent throughout the day, often worsening at night, and wearingthe TENS device on the upper calf makes it discreet and unobtrusive,which encourages more regular use.

As mentioned above, the novel TENS device disclosed in pending priorU.S. patent application Ser. No. 14/230,648 (and published as U.S.Patent Application Publication No. US 2014/0296934 A1), which isdesigned for use during sleep, detects when the user is asleep andadjusts the therapeutic stimulation level to avoid disturbing sleep. Itwould be advantageous for a TENS device aimed at improving sleep qualityto also quantify sleep quality and sleep disorders, since users will bemore likely to use the TENS device if they are aware of, and convincedof, its benefit to their sleep.

The gold standard in determining the sleep-wake state of a subject ispolysomnography which comprises at least three distinct types of data,i.e., electroencephalogram (EEG), electrooculography (EOG) andelectromyography (EMG). Because of the difficulty in recording andanalyzing these types of data, actigraphy has been developed and refinedover the last 30 years as a practical alternative to study sleep/awakepatterns. Actigraphy is a continuous recording of body movement by meansof a body-worn device, typically equipped with accelerometers[Ancoli-Israel S, Cole R, Alessi C, Chambers M, Moorcroft W, Pollak C P.The role of actigraphy in the study of sleep and circadian rhythms.Sleep. May 1 2003; 26(3):342-392].

Wearable electronic devices for health and fitness have becomewidespread, and most have accelerometers and, from acceleration data,compute various metrics of activity either to track daytime activitiesor to quantify sleep patterns. Most of these actigraphy-based devicesare worn on the wrist however, and in certain ways that limits theirability to detect and quantify sleep.

SUMMARY OF THE INVENTION

Significantly, it has now been recognized that the placement of a novel,accelerometer-equipped TENS device on the upper calf, with tightmechanical coupling to the upper calf, may be used to support novelapproaches for detecting when the user is asleep, and novel metrics foranalyzing the sleep of the user, and novel approaches to quantify bodyand leg motions associated with poor sleep quality and/or disorders suchas restless leg syndrome, and novel approaches for providing enhancedtranscutaneous electrical nerve stimulation (TENS) using the same. Amongthese novel metrics are “leg movements”, “body roll events” associatedwith rolling over in bed, and “time-on-back” which is relevant to userssuffering not only from chronic pain but also from problematic sleeppositions which can cause snoring or sleep apnea. In addition totracking and reporting sleep indicators, real-time feedback to the userbased on indicator trends can also help the user to improve sleepquality. An example is to provide an alert (via mechanical or electricalmeans, for example) to the user when time-on-back duration exceeds athreshold. Another example is to alter TENS stimulation parameters whenleg movement patterns associated with discomfort caused by nighttimepain are detected in order to enhance the analgesic effect of TENStherapy.

Thus, the present invention comprises the provision and use of a novelTENS device which comprises a TENS stimulator designed to be placed onthe user's upper calf and a pre-configured electrode array designed toprovide circumferential stimulation to the upper calf of the user. Athree-axis (x, y, z) accelerometer incorporated in the TENS devicecontinuously measures the projection of static gravity onto each axis(i.e., x, y, z), which depends on the device orientation, andtime-varying acceleration on each axis due to user motion along thataxis.

The placement of the novel TENS device on the upper calf of the user isused to support novel approaches for detecting when the user is asleep,and for quantifying sleep and assessing abnormal body and leg motions,and for providing enhanced TENS therapy using such sleep analysis.

First, the novel TENS device measures leg orientation, which is highlycorrelated with body orientation and therefore indicative of the user'srecumbent state (and thereby the user's sleep-wake state). Specifically,the novel TENS device measures two distinct aspects of leg orientation:leg “elevation” (or the angle of the lower leg relative to thehorizontal), and leg “rotation” (or the angle of rotation of the lowerleg about its own axis).

Second, the novel TENS device measures leg motion, which is alsoindicative of the user's sleep-wake state. Specifically, the novel TENSdevice measures two distinct aspects of leg motion: “net activity”(which is the magnitude of movement-related acceleration averaged withinone-minute windows), and “leg movements” (or brief events that are knownto occur in sleep but are not evident in net activity). Some legmovements accompanied by a large leg rotation may be further classifiedas “body roll events” (such as occur when rolling over in bed).Repetitive leg movements may occur in people with chronic pain and othermedical conditions, and may degrade the quality of sleep experienced bythe person (and his/her sleep partner). Quantification and monitoring ofthe repetitive leg movements may provide insights to these conditionsand trends of these conditions.

Third, the novel TENS device combines these two measures of legorientation (i.e., leg elevation and leg rotation) and two measures ofleg motion (i.e., net activity and leg movements) to improve sleepquantification and to utilize more precise quantification metrics toenhance therapeutic benefits.

The determination of sleep-wake state by the novel TENS device proceedsin several steps. The user is considered to be “in-bed” if the user'sleg orientation is determined to be recumbent (i.e., near horizontal)for a selected portion (e.g., a majority) of a selected time period(e.g., a decision window). During the in-bed state, “sleep onset” isdefined as the first time that the user's net activity and leg movementsfall below set thresholds for a specified period of time (e.g., adecision window). Following sleep onset, the novel TENS device measuresnet activity and leg movements. During all of the time intervals inwhich the net activity is below some specified threshold, the user isconsidered to be “asleep”. During all of the time in which the user isrecumbent, the net activity is below some net activity threshold, thenumber of leg movements is below some leg movement threshold, and thenumber of body rolls is zero, the user is considered to be “restful”.During all of the time in which the static leg rotational angle fallsbetween two static leg rotational angle thresholds, the user isconsidered to be sleeping “on-back”. These times, and the ratios ofthese times, may be used to compute measures of “sleep duration” and“sleep quality”. This sleep analysis may then be reported (e.g., to theuser and/or to the care provider of the user) and/or used to provideenhanced TENS therapy to the patient.

In one preferred form of the present invention, there is providedapparatus for providing transcutaneous electrical nerve stimulation(TENS) therapy to a user, said apparatus comprising:

a housing;

an application unit for providing mechanical coupling between saidhousing and the user's body;

a stimulation unit for electrically stimulating at least one nerve ofthe user;

a sensing unit for sensing the user's body movement and bodyorientation; and

a reporting unit for providing the user with feedback based on theuser's sensed body movement and body orientation.

In another preferred form of the present invention, there is provided amethod for applying transcutaneous electrical nerve stimulation to auser, said method comprising the steps of:

applying a stimulation unit and a sensing unit to the user's body;

using the stimulation unit to deliver electrical stimulation to the userto stimulate one or more nerves;

analyzing electromechanical sensing data from the sensing unit toquantify the user's body orientation and body activity levels; and

modifying the electrical stimulation delivered by the stimulation unitbased on the user's body orientation and body activity levels.

In another preferred form of the present invention, there is providedapparatus for monitoring the sleep patterns of a user, said apparatuscomprising:

a housing;

an application unit for providing mechanical coupling between saidhousing and the user's body;

a sensing unit disposed within the housing to sense the user's bodymovement and body orientation; and

a reporting unit for providing the user with feedback based on theuser's sensed body movement and body orientation.

In another preferred form of the present invention, there is provided amethod for monitoring the sleep patterns of a user, said methodcomprising of the steps of:

applying a sensing unit and a feedback unit to the user body;

using the sensing unit to determine the user's body movement and bodyorientation; and

providing the user with feedback via said feedback unit based on bodyactivity and body orientation.

In another preferred form of the present invention, there is providedapparatus for providing transcutaneous electrical nerve stimulation(TENS) therapy to a user, said apparatus comprising:

a housing;

an application unit for providing mechanical coupling between saidhousing and the user's leg;

a stimulation unit for electrically stimulating at least one nerve ofthe user; and

a sensing unit for sensing the user's leg orientation and leg motion,wherein sensing the user's leg orientation comprises determining theuser's leg elevation and leg rotation, and further wherein sensing theuser's leg motion comprises determining the user's net activity and legmovements; and

a controller for modulating said stimulation unit based on thedeterminations made by said sensing unit.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and features of the present invention will bemore fully disclosed or rendered obvious by the following detaileddescription of the preferred embodiments of the invention, which is tobe considered together with the accompanying drawings wherein likenumbers refer to like parts, and further wherein:

FIG. 1 is a schematic view showing a novel TENS device formed inaccordance with the present invention, with the novel TENS device beingmounted to the upper calf of a user;

FIG. 2 is a schematic view showing the novel TENS device of FIG. 1 ingreater detail;

FIG. 3 is a schematic view of the novel TENS device shown in FIGS. 1 and2 attached to the tissue of a patient;

FIG. 4 is a schematic view of the novel TENS device of FIGS. 1 and 2,including its user state (i.e., leg orientation and leg motion)detector;

FIG. 5 is a schematic view showing the on-skin detection system of thenovel TENS device shown in FIGS. 1 and 2, as well as its equivalentcircuits when the novel TENS device is on and off the skin of a user;

FIG. 6 is a schematic view showing the orientation of the accelerometerincorporated in the novel TENS device of FIGS. 1 and 2, when the novelTENS device of FIG. 1 is applied to the upper calf of a user;

FIG. 7 is a schematic view showing the relationship betweengravitational force vector g and the accelerometer y-axis in the novelTENS device when the novel TENS device (applied to upper calf of theuser) rests at an elevation angle θ with respect to the horizontalplane;

FIG. 8 is a schematic view showing the detection of a leg movement (LM)event, and calculation of the change Δφ in device rotational angle φafter (vs. before) the LM event;

FIG. 9 is a schematic view showing the mathematics for relating theaccelerometer rotational angle φ (measured by the accelerometer) to theleg rotational angle β, via a third angle α representing the rotationalposition of the novel TENS device on the upper calf of a user; and

FIG. 10 is a schematic flow chart showing exemplary operation of thenovel TENS device, including its user state (i.e., leg orientation andleg motion) detector.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The Novel TENS Devicein General

FIG. 1 illustrates a novel TENS device 100 formed in accordance with thepresent invention, with the novel TENS device being shown worn on auser's upper calf 140. A user may wear TENS device 100 on either leg.

TENS device 100 is shown in greater detail in FIG. 2 and preferablycomprises three primary components: a stimulator 105, a strap 110, andan electrode array 120 (comprising a cathode electrode and an anodeelectrode appropriately connected to stimulator 105 as is well known inthe art). Stimulator 105 preferably comprises three mechanically andelectrically inter-connected compartments 101, 102, and 103.Compartments 101, 102, 103 are preferably inter-connected by hingemechanisms 104 (only one of which is shown in FIG. 2), thereby allowingTENS device 100 to conform to the curved anatomy of a user's leg. In apreferred embodiment of the present invention, compartment 102 housesthe TENS stimulation circuitry (except for a battery) and user interfaceelements 106 and 108. Compartment 102 also houses an accelerometer 152(see FIGS. 4 and 6), preferably in the form of a semiconductor chipaccelerometer, for detecting user gestures, user leg and bodyorientation, and user leg and body motion, as will hereinafter bediscussed. Compartment 102 also houses a real-time clock 505 (FIG. 4).In a preferred embodiment, compartments 101 and 103 are smaller,auxiliary compartments that house a battery for powering the TENSstimulation circuitry and other circuitry, and other ancillary elements,such as an ambient light sensor or detector 510 (FIGS. 4 and 6) fordetermining ambient light conditions, and a wireless interface unit ofthe sort well known in the art (not shown) for allowing TENS device 100to wirelessly communicate with other elements (e.g., a hand-heldelectronic device such as a smartphone 860). In another embodiment ofthe present invention, only one or two compartments may be used forhousing all of the TENS stimulation circuitry, battery, and otherancillary elements of the present invention. In another embodiment ofthe present invention, a greater number of compartments are used, e.g.,to conform better to the body and to improve user comfort. In anotherembodiment of the present invention, a flexible circuit board is used todistribute the TENS stimulation circuitry and other circuitry moreevenly around the leg and thereby reduce bulk.

Still looking now at FIG. 2, user interface element 106 preferablycomprises a push button for user control of electrical stimulation, anduser interface element 108 preferably comprises an LED for indicatingstimulation status and for providing other information to the user.Additional user interface elements (e.g., a multi-LED array, LCDdisplay, audio feedback through a beeper or voice output, haptic devicessuch as a vibrating motor, etc.) may also be provided and are consideredto be within the scope of the present invention.

The preferred embodiment of the present invention is designed to be wornon the upper calf 140 of the user as shown in FIG. 1. TENS device 100,comprising stimulator 105, electrode array 120, and strap 110, issecured to upper calf 140 by placing the apparatus in position and thentightening strap 110. Although the preferred embodiment of the presentinvention comprises placement of the TENS device on the upper calf ofthe user, additional anatomical locations (such as above the knee, onthe lower back, and on the upper arm) are also contemplated and are alsoconsidered to be within the scope of the present invention.

FIG. 3 is a schematic representation of the current flow between TENSdevice 100 and the user. As seen in FIG. 3, stimulation current 415 froma constant current source 410 flows into the user's tissue 430 (e.g.,the user's upper calf) via anode electrode 420. Anode electrode 420comprises a conductive backing (e.g., silver hatch) 442 and hydrogel444. The current passes through the user's tissue 430 and returns toconstant current source 410 through cathode electrode 432 (cathodeelectrode 432 also comprises a conductive backing 442 and hydrogel 444).Constant current source 410 preferably provides an appropriate biphasicwaveform (i.e., biphasic stimulation pulses) of the sort well known inthe art of TENS therapy. In this respect it should be appreciated thatthe designation of “anode” and “cathode” electrodes is purely notationalin the context of a biphasic waveform (i.e., when the biphasicstimulation pulse reverses its polarity in its second phase of thebiphasic TENS stimulation, current will be flowing into the user's bodyvia “cathode” electrode 432 and out of the user's body via “anode”electrode 420).

Further details regarding the construction and use of the foregoingaspects of TENS device 100 are disclosed in (i) U.S. Pat. No. 8,948,876,issued Feb. 3, 2015 to NeuroMetrix, Inc. and Shai N. Gozani et al. forAPPARATUS AND METHOD FOR RELIEVING PAIN USING TRANSCUTANEOUS ELECTRICALNERVE STIMULATION (Attorney's Docket No. NEURO-5960), which patent ishereby incorporated herein by reference, and (ii) pending prior U.S.patent application Ser. No. 14/230,648, filed Mar. 31, 2014 by Shai N.Gozani et al. for DETECTING CUTANEOUS “ELECTRODE PEELING” USINGELECTRODE-SKIN IMPEDANCE (Attorney's Docket No. NEURO-64), published asU.S. Patent Application Publication No. US 2014/0296934 A1 on Oct. 2,2014, which patent application is hereby incorporated herein byreference.

The User State (i.e., Leg Orientation and Leg Motion) Detector

In accordance with the present invention, TENS device 100 furthercomprises (e.g., within compartment 102) user state (i.e., legorientation and leg motion) detector 500 for (i) determining thesleep-wake state of the user, (ii) analyzing the sleep of the user,and/or (iii) providing enhanced transcutaneous electrical nervestimulation (TENS) using the same. To this end, and looking now at FIG.4, user state (i.e., leg orientation and leg motion) detector 500generally comprises the aforementioned accelerometer 152, theaforementioned real-time clock 505, the aforementioned ambient lightdetector 510, a processor 515 for calculating user activity (e.g., bodyorientation, body movement and activity levels), and a controller 520for modifying the stimulation current provided by the constant currentsource 410 of TENS device 100 in accordance with determinations made byprocessor 515.

When the TENS device is secured in position on the user's upper calf,the position and orientation of accelerometer 152 (FIGS. 4 and 6) ofTENS device 100 is fixed relative to the lower limb of the user. Tightmechanical coupling between TENS device 100 and lower limb 140 allowsmovement of the user's lower limb to be accurately measured byaccelerometer 152. Such tight mechanical coupling is preferablyestablished through the aforementioned strap 110. Alternatively, tightmechanical coupling may be established through other means, e.g., aflexible band encasing the TENS device. If desired, a tension gauge 109(FIG. 1) may be provided on strap 110 to confirm that a tight mechanicalcoupling is established between TENS device 100 and upper calf 140.

Data from accelerometer 152 are analyzed in real time by processor 515of user state (i.e., leg orientation and leg motion) detector 500 todetermine the orientation and motion of the lower limb (i.e., upper calf140) of the user. The orientation, motion, and activity level of thelower limb (i.e., upper calf 140) of the user, determined by analyzingthe data from accelerometer 152, are used to determine the sleep-wakestate and sleep patterns of the user. Based on the sleep-wake state andsleep patterns, TENS device 100 can modify its stimulation pattern (suchas the stimulation intensity level and the onset of the stimulation) viacontroller 520, or provide the user with additional feedback (such asmechanical vibration if the duration of the sleep-on-back state exceedsa threshold).

The leg orientation and leg motion components measured by the user state(i.e., leg orientation and leg motion) detector 500 of the presentinvention may individually or collectively contribute to thedetermination of the sleep-wake state of the user. In one preferred formof the invention, processor 515 of TENS device 100 measures the calforientation of the user, which is highly correlated with the bodyorientation of the user. More particularly, upright body orientation isgenerally a reliable indicator that the user is in a wake state, whilerecumbent orientation suggests a resting state (e.g., such as occursduring sleep). Regular and robust body movement is more likely theresult of user activities during the daytime (i.e., during wake state),while quiet or low-level spontaneous movements are more likely duringnighttime (i.e., during sleep state). Interactions of body orientationand movement level can also be useful in identifying the sleep-wakestate of the user (i.e., thereby enhancing a sleep-wake stateclassification). Specifically, recumbent body orientation and alow-level of physical activity is generally a good indicator that theuser is asleep.

In addition, real-time clock 505 of user state (i.e., leg orientationand leg motion) detector 500 allows assigning a nontrivial a prioriprobability of the sleep-wake state at any given time of the day inorder to further refine the sleep-wake state classification resultsobtained by the aforementioned analysis of leg orientation and legmotion data (i.e., a user is more likely to be asleep at 3:00 am andless likely to be asleep at 4:00 pm). In a preferred embodiment of thepresent invention, to reflect that the a priori probability that thesleep state is low at a specific daytime window, the threshold value forclassifying user body orientation as recumbent can be made morestringent.

In another embodiment of the present invention, output from ambientlight sensor 510 is used to improve sleep-wake classification results.The ambient light sensor 510 can be used to determine if the user is inan environment which has an illuminated or non-illuminated ambience, toreflect the a priori probability that a user is more likely to besleeping in a dark setting than in a brightly lit setting. Accordingly,the threshold values for classifying user body position and motion levelcan be adjusted to reflect the a priori probability of sleep.

On-Skin Detector

In one preferred form of the invention, TENS device 100 may comprise anon-skin detector to confirm that TENS device 100 is firmly seated on theskin of the user.

More particularly, the orientation and motion measures fromaccelerometer 152 in TENS device 100 only become coupled with theorientation and motion of a user when the TENS device is worn by theuser. In a preferred embodiment, an on-skin detector 521 is provided todetermine whether and when TENS device 100 is securely placed on theuser's upper calf. In the preferred embodiment, and looking now at FIG.5, on-skin detector 521 may be provided within TENS device 100. Moreparticularly, in one preferred form of the invention, a voltage of 20volts from voltage source 204 is applied to the anode terminal 212 ofTENS stimulator 105 by closing the switch 220. If the TENS device isworn by the user, then user tissue 430, interposed between anodeelectrode 420 and cathode electrode 432, will form a closed circuit toapply the voltage to the voltage divider circuit formed by resistors 208and 206. More particularly, when TENS device 100 is on the skin of theuser, the equivalent circuit 260 shown in FIG. 5 represents thereal-world system and equivalent circuit 260 allows the anode voltageV_(a) 204 to be sensed through the voltage divider resistors 206 and208. The cathode voltage measured from the amplifier 207 will benon-zero and close to the anode voltage 204. On the other hand, whenTENS device 100 is not on the skin of the user, the equivalent circuit270 represents the real-world system and the cathode voltage fromamplifier 207 will be zero.

On-skin detector 521 is preferably employed in two ways.

First, if on-skin detector 521 indicates that electrode array 120 ofTENS device 100 has become partially or fully detached from the skin ofthe user, TENS device 100 can stop applying TENS therapy to the user.

Second, if on-skin detector 521 indicates that electrode array 120 ofTENS device 100 has become partially or fully detached from the skin ofthe user, processor 515 of TENS device 100 will recognize that the datafrom accelerometer 152 may not reliably reflect user leg orientation andleg motion, and user state (i.e., leg orientation and leg motion)detector 500 can take appropriate action (e.g., alert the user). In thisrespect it should be appreciated that, when the on-skin detector 521indicates that TENS device 100 is on the skin of the user, andaccelerometer 152 is closely coupled to the lower limb of the user, thedata from accelerometer 152 may be representative of user legorientation and user leg motion. However, when the on-skin detector 521indicates that TENS device 100 is not on the skin of the user,accelerometer 152 is not closely coupled to the lower limb of the user,and the data from accelerometer 152 will not be representative of userleg orientation and user leg motion.

Accelerometer Data Processing

In one preferred form of the invention, user state (i.e., legorientation and leg motion) detector 500 comprises a processor 515 fortaking the accelerometer data from accelerometer 152 and calculatinguser activity (e.g., body orientation, body movement and activitylevels).

More particularly, in one preferred form of the invention, processor 515uses the accelerometer data from accelerometer 152 to measure the user'sleg orientation, which is highly correlated with body orientation andtherefore indicative of the user's recumbent state (and thereby theuser's sleep-wake state); and processor 515 uses the accelerometer datafrom accelerometer 152 to measure the user's leg motion, which is alsoindicative of the user's sleep-wake state and leg motion activitylevels; and processor 515 uses the determinations of user legorientation and user leg motion to enhance sleep quantification.

More particularly, processor 515 uses the accelerometer data fromaccelerometer 152 to measure two distinct aspects of the user's legorientation: leg “elevation” (or the angle of the lower leg relative tothe horizontal plane), and leg “rotation” (or the angle of rotation ofthe lower leg about its own axis).

And processor 515 uses the accelerometer data from accelerometer 152 tomeasure two distinct aspects of leg motion: “net activity” (which is themagnitude of movement-related acceleration averaged within one-minutewindows), and “leg movements” (or brief events that are known to occurin sleep but are not evident in net activity). Some leg movementsaccompanied by a large leg rotation may be further classified as “bodyroll events” (such as occur when rolling over in bed).

In a preferred embodiment of the present invention, processor 515 forcalculating user activity (e.g., body orientation, body movement andactivity levels) is constructed and configured to operate as follows.Raw accelerometer data produced at 400 Hz are decimated to 50 Hz.Following that, the time scale of an “instant” is defined to be equal to0.1 sec. The 50 Hz data on each axis (x, y, z) are separately averagedover each instant, to provide a low-noise data stream at 10 Hz, denotedby A_(x)(t), A_(y)(t), and A_(z)(t).

The accelerometer data A_(x)(t), A_(y)(t), and A_(z)(t) are used to formfeatures which are averages of A_(x)(t), A_(y)(t), and A_(z)(t) over alonger time window (e.g., a one minute window) to capture thesteady-state projection of earth gravity along each axis (x, y, z).These features are used for detecting leg orientation (i.e., legelevation and leg rotation).

Additionally, the accelerometer data A_(x)(t), A_(y)(t), and A_(z)(t)are high-pass filtered to remove the static gravity component in orderto isolate acceleration components caused by leg movement. The high-passfilter has −3 dB point at 0.5 Hz. High-pass filtered accelerometer dataare denoted Ã_(x)(t), Ã_(y)(t), and Ã_(z)(t).

Leg Elevation Detection

In one preferred form of the invention, user state (i.e., legorientation and leg motion) detector 500 is configured to detect legelevation.

More particularly, in order to determine the “body orientation state”for the purpose of sleep monitoring, the present invention uses the legelevation, which is computed by processor 515 of user state (i.e., legorientation and leg motion) detector 500, based on measurement data fromaccelerometer 152 when TENS device 100 is placed on the user's uppercalf 140 (FIG. 1). In a preferred embodiment, and looking now at FIG. 6,accelerometer 152 is located on the circuit board 151 of the TENScircuitry housed inside compartment 102, so that the accelerometer's3-axis directions, shown at 153 in FIG. 6 (i.e., x-axis, y-axis,z-axis), are known and fixed in relationship to the lower leg when theTENS device is placed on the user's upper calf: the y-axis is alignedlongitudinally along the longitudinal axis of the lower leg; the x-axisis disposed tangential to the surface of the lower leg and perpendicularto the y-axis, and the z-axis points radially away from the surface ofthe lower leg.

A stationary upright user, or one sitting with feet resting on theground, will have an upright calf elevation. Consequently, the y-axisacceleration of accelerometer 152 will have a value of about −1 g due toEarth gravity 154 (FIG. 6), where g is the acceleration due to Earthgravity. The above measurement holds true regardless of the exactrotational position 160 of compartment 102 around upper calf 140. WhenTENS device 100 is placed upside down on the upper calf, which is apossible placement position, the accelerometer axes rotate as shown at155 in FIG. 6. In this case, a stationary upright user will have ameasured acceleration value along the y-axis of about +1 g. By contrast,a stationary recumbent user lying with legs elevated on a bed will havea measured acceleration value along the y-axis of about 0 g. In apreferred embodiment, if the absolute value of the y-axis accelerationmeasurement is greater than a threshold level, then the leg elevation isconsidered to be upright, otherwise the leg elevation is considered tobe recumbent.

Looking now at FIG. 7, where the Earth's gravitational vector isdownward, the elevation angle θ (172) represents the angle between thepositive accelerometer y-axis direction (174) and the true horizontalplane (170). In a preferred embodiment, the y-axis accelerationmeasurement threshold level is set to 0.50 g, corresponding to a legelevation angle θ≈30° from the horizontal plane, however, otherthreshold values may also be used, and users may have the option ofadjusting this value to better distinguish their sleep and wakebehaviors.

In general, the acceleration measured along the y-axis will include notonly the projection of gravity onto that axis, but also a contributionfrom motion:

A _(y)(t)=±sin |θ(t)|+m(t) [in unit of g]

where t is time, and m(t) is the contribution due to leg motion. Thespecific ± sign depends upon the TENS device placement on upper calf 140and is fixed for each placement. The motion component m(t) is considered“noise” in the context of determining leg elevation, and will have zeromean over a sufficiently large window.

In a preferred embodiment, a leg elevation algorithm, taking intoaccount user body movement, is implemented by processor 515 of userstate (i.e., leg orientation and leg motion) detector 500 in thefollowing manner.

Step 1. Set a target angle threshold θ₀ (this is the “Threshold1” shownat step 910 in FIG. 10) for the angle θ so that |θ|<θ₀ corresponds tothe case where the upper calf 140 of the user is recumbent. In apreferred embodiment, the target angle threshold θ₀ is set to 30°.

Step 2. Define non-overlapping windows of length N, called “epochs”. Thetime at the end of each epoch is denoted T. In a preferred embodiment,the accelerometer data (in units of g, standard earth gravity) aresegmented into epochs, i.e., one-minute windows. With an accelerometerdata rate of 10 Hz, the epoch length is N=600. The mean A_(y,T) and thestandard error of the mean SE_(Y,T) are calculated based on samples ineach epoch.

Step 3. Let θ_(T)=sin⁻¹A_(y,T). Values of θ_(T)≈θ₀ can lead to erraticswitching of the leg elevation state. In order to reduce this, define ahysteresis band θ₀±θ_(H). In the preferred embodiment, the hysteresisparameter θ_(H) is set to 2.50, but other values are possible (butshould be small compared to θ₀). In the preferred embodiment, ratherthan computing sin⁻¹ for every epoch, the angular thresholds are insteadconverted to acceleration units, i.e., by computing two thresholdsA_(±)=sin(θ₀±θ_(H)), against which A_(y,T) will be compared.

Step 4. The ability of the hysteresis band to prevent erratic switchingof the leg elevation state depends upon the amount of noise in the data,characterized by SE_(Y,T), which is the standard error of the meanA_(y,T). In order to account for the noise level in the data, processor515 of user state (i.e., leg orientation and leg motion) detector 500,processor 515 compares the acceleration data A_(y,T) to the thresholdsA_(±). However, instead of comparing the mean A_(y,T) per se to thethresholds A_(±), processor 515 compares the “confidence interval”A_(y,T)±ηSE_(Y,T) to the thresholds A_(±). More specifically, for eachepoch, if the prior elevation state was recumbent, in order to classifythe next state as upright, processor 515 of user state (i.e., legorientation and leg motion) detector 500 requires[|A_(y,T)|−ηSE_(Y,T)]>A₊. If the prior elevation state was upright, inorder to classify the next state as recumbent, processor 515 of userstate (i.e., leg orientation and leg motion) detector 500 requires[|A_(y,T)|+ηSE_(Y,T)]<A⁻. In a preferred embodiment η=3, but othervalues are possible.

Instantaneous Activity

In one preferred form of the invention, processor 515 of user state(i.e., leg orientation and leg motion) detector 500 may be configured todetect instantaneous activity.

More particularly, when TENS device 100 is worn on the user's upper calf140, the user's activity will be captured by accelerometer 152 of theTENS device. Each axis (x, y, z) of accelerometer 152 measures theprojection of the acceleration vector along that axis. As describedabove, the measured acceleration includes the static effect of earthgravity, as well as contributions from leg movement. In order to isolatethe contributions from leg movement, processor 515 of user state (i.e.,leg orientation and leg motion) detector 500 high-pass filters theinstant data vector A(t)=[A_(x)(t),A_(y)(t),A_(z)(t)] before furtherprocessing.

Although the acceleration component for each individual axis of theaccelerometer contains unique and useful information for body movementanalysis, the vector magnitude of acceleration, called the“instantaneous acceleration”, denoted Ã_(I)(t) and defined in equationbelow, is commonly used to quantify the overall motion-related activity:

Ã _(I)(t)=√{square root over (Ã _(X)(t)² +Ã _(Y)(t)² +Ã _(Z)(t)²)}

In a preferred embodiment of the present invention, processor 515 ofuser state (i.e., leg orientation and leg motion) detector 500 uses thisinstantaneous acceleration Ã_(I)(t) for the actigraphy calculations.However, calculations based on other combinations of acceleration axesmay also be used. For example, rather than combining all three axesequally as done with Ã_(I)(t) as defined above, only some axes may beused, or certain axes may be contrasted through subtraction.

Leg Movement Detector

In one preferred form of the invention, processor 515 of user state(i.e., leg orientation and leg motion) detector 500 may be configured todetect leg movement.

More particularly, the instantaneous acceleration Ã_(I)(t) is a timeseries comprised of brief events, such as leg movements known to occurduring normal and abnormal sleep, and sustained activity, such as occursduring walking, running, or climbing stairs. In a preferred embodiment,leg movements (LM) are computed in a manner that is consistent with thedetection of periodic leg movements (PLM) defined in the clinicalliterature (Bonnet et al, 1993; Zucconi et al, 2006), however, otherapproaches to detecting brief leg movements are possible and areconsidered to be within the scope of the present invention.

In the preferred embodiment, a leg movement (LM) detection algorithm isimplemented by processor 515 of user state (i.e., leg orientation andleg motion) detector 500 in the following manner.

Step 1. Define two thresholds (these are the “Threshold2” and“Threshold3” shown at steps 914 and 918, respectively, in FIG. 10) thatthrough data analysis are found to be sensitive and specific to briefleg movements. In the preferred embodiment, and appropriate to thevariance properties of the data measured by the accelerometer 152, thesethresholds are 0.02 g (816 in FIG. 8) and 0.03 g (815 in FIG. 8), butother values may also be used.

Step 2. Define an instantaneous activity state (IAS) and initialize theIAS to False.

Step 3. Compute instantaneous acceleration Ã_(I)(t) for each timeinstant.

Step 3. Update the IAS for each time instant as follows. If IAS=Falseand Ã_(I)(t)>0.03 g, then set IAS=True. If IAS=True and Ã_(I)(t)<0.02 g,then set IAS=False. Two thresholds used in this way implement hysteresisin a simple way to prevent rapid switching in the IAS.

Step 4. When IAS becomes True, a leg movement (LM) period begins. WhenIAS becomes false and remains false for more than 0.5 second, the LMperiod ends. Thus a contiguous time interval in which IAS=True, andsurrounded by intervals in which IAS=False, comprises a leg movement(LM) period. However, if contiguous intervals for which IAS is True areseparated by less than 0.5 second, the brief interval for which IAS wasFalse is ignored.

The top panel (810) in FIG. 8 shows an example of the leg movement (LM)detection algorithm applied to real data. Time is measured in instants,i.e., steps of 0.1 second. The dots, and the line 812 connecting them,are the instantaneous accelerations Ã_(I)(t). The vertical line 813 iswhen Ã_(I)(t) first went above the threshold 815 (threshold value=0.03g), at which point IAS was set to True. The instantaneous accelerationsÃ_(I)(t) fell below the second threshold 816 (threshold value=0.02 g)before the 90^(th) instant. However, their durations were shorter than0.5 second so they were ignored and the LM period continued. Thevertical line 814 shows the instant when Ã_(I)(t) first went below thesecond threshold 816 for more than 0.5 second so the LM period wasterminated. The net result is an LM period with a duration of 89instants (i.e., 8.9 seconds).

Body Roll Detector

In one preferred form of the invention, processor 515 of user state(i.e., leg orientation and leg motion) detector 500 is configured tofunction as a body roll detector.

More particularly, when the TENS device 100 (FIG. 9) is worn on thelower leg (i.e., upper calf 140) of a user, its accelerometer 152 willsense the projection of the gravity in its x-z plane when the user is ina recumbent position. The angle φ between the device x-axis and thegravity vector −g can be calculated based on the projected gravity valuein the x and z axis. Axis z′ is aligned with the “big toe” direction ofthe user's leg to which the TENS device 100 is attached. Angle α betweenthe device z-axis and the leg x′-axis is fixed when the TENS device issecurely placed on the lower leg (i.e., upper calf 140) of the user.Finally, the body orientation angle β defines the relative rotationalposition between the leg (defined as the direction in which the big toeis pointed, i.e., the z′-axis) and the earth gravity (z″-axis). Theangular value remains the same when measuring from the x′-axis to thex″-axis. It is straightforward to derive the relationship between β andφ as follows:

β=180−α−φ

Because the angle α is fixed, the leg rotation angle β can be derivedfrom the angle φ as measured by the accelerometer 152.

Some brief increases in activity that are classified as leg movement(LM) are associated with large changes in the roll angle φ measured bythe TENS device 100. Rolls of sufficient magnitude are unlikely toinvolve only the leg, but rather are likely to indicate that the entirebody is rolling over while in bed, e.g., from the left side to the rightside, or from the back to the left side or the right side. Some legmovements (LMs) may therefore be classified as “body roll events”.

In one preferred embodiment, a body roll detection algorithm isimplemented by processor 515 in user state (i.e., leg orientation andleg motion) detector 500, using only the angle change Δφ, in thefollowing manner:

Step 1. For each LM period detected, select the raw acceleration vectorA(t) in short windows before and after the leg movement. In a presentinvention, this window is an instant (0.1 seconds).

Step 2. Before and after each LM period, take the instant values of A(t)(not high-pass filtered) on each axis separately so as to obtainA_(x)(t), A_(y)(t), and A_(z)(t).

Step 3. Using these values before and after the LM, compute the rotationangle φ(t)=a tan 2{A_(x)(t), A_(z)(t)}. The inverse tangent function atan 2 returns an angle in the range −180°<φ(t)≦180°, i.e., a result inall four possible quadrants.

Step 4. Compute the change in rotational angle Δφ=φ_(after)−φ_(before).In order to facilitate comparison with a threshold (this is the“Threshold4” shown at step 924 in FIG. 10), this difference is put inthe range −180°<Δφ≦180°, i.e., if Δφ>180° then subtract 360°, but ifΔφ≦−180° then add 360°.

Step 5. Compare the absolute value |Δφ| with a threshold value. In thepresent invention, this threshold value is 50°, but other values may beused. If |Δφ|>50°, then classify the LM event as a “body roll event”.

The middle panel (820) in FIG. 8 shows this body roll detectionalgorithm applied to real data. The acceleration values A_(x)(t),A_(y)(t), and A_(z)(t) are plotted in traces 821, 822, and 823. They-axis component A_(y)(t)≈0 g throughout the event, consistent with thecondition that lower leg elevation is in recumbent state. In contrast,A_(x)(t) and A_(z)(t) show significant activities, especially betweentime instants 30 and 70. In addition, the steady state value forA_(x)(t) changed from +1 g (before the LM period) to −1 g (after the LMperiod), suggesting a body roll event.

The bottom panel (830) of FIG. 8 shows the calculation of the elevationangle θ (833) and the rotation angle φ (834) for each instant. Theelevation angle θ≈0 throughout the event, consistent with the lower legbeing in recumbent elevation. In contrast, the rotation angle φ changesfrom φ+90° (indicated by the empty circle 831) to φ≈−88° (indicated bythe filled circle 832). The angular change is Δφ≈178°, consistent with a(rightward) roll of the entire body.

These body rolls may be reported directly to the user to inform themabout their sleep patterns. In addition, because body roll events may bebrief, the associated increase in activity may not be evident in theepoch average of activity, and therefore may not cause that epoch to beclassified as awake. Although rolling over in bed may not indicate anawake state, it does indicate momentarily restless sleep. This novelapproach for detecting body rolls by evaluating changes in roll anglesassociated with brief leg movement (LM) permits the differentiation ofleg movement associated with no body rolls from leg movement associatedwith body rolls, and thus provides a finer description of sleep patternsthat are helpful in clinical diagnosis.

In another preferred embodiment, rather than using single instants ofA(t) before and after the LM to compute the angles φ, the mean or medianvalues of A(t) over several instants before and after the LM are used toimprove robustness to noise.

In another preferred embodiment, a body roll detection algorithm isimplemented by processor 515 of user state (i.e., leg orientation andleg motion) detector 500 using the angle change Δβ in the followingmanner. Consider a person lying on their back, with the TENS deviceplaced on their right leg. Recalling that, with the TENS device placedon either leg, β=0 when the toes are pointed vertically upward, and βincreases with counterclockwise (CCW) rotation, therefore the mostlikely range of leg rotational positions is −80°≦β≦0°. Any change inangle Δβ that remains within that range may not likely be associatedwith a body roll. In contrast, a change in angle Δβ from inside thatrange to outside that range is most likely associated with a body roll.In this way, using the change in angle Δβ, the threshold for detecting abody roll may be adjusted depending upon the leg on which the device isplaced. That is to say, in addition to the magnitude of the change Δβ,the value of the leg rotation angle β before and after the leg movement(LM), and the sign of the angle change Δβ across the leg movement (LM),may be used to improve performance of the body roll detector.

Static Body Rotational Position Detector

In one preferred form of the invention, processor 515 of user state(i.e., leg orientation and leg motion) detector 500 may be configured tofunction as a static body rotational position detector.

More particularly, users with sleep apnea are recommended not to sleepon their back.

Because of the limited rotational range of motion of the human hip, legrotational position is highly correlated with body position, e.g., whensleeping on one's back, the toes of either foot are pointed upward abovethe horizontal plane to varying degrees, not likely exactly on thehorizontal plane, and never below the horizontal plane. Thisobservation, together with the placement of the novel TENS device on theupper calf of the user, allows an innovative addition to sleep analysis.

The time scale of an “epoch” equal to one minute, and the epoch-averagednon-high-pass filtered acceleration values Ā_(X,T)(t), Ā_(Y,T)(t), andĀ_(Z,T)(t) were introduced above in the section entitled “Leg ElevationDetection”. Because it is sufficient to report the time spent sleepingon the back at the resolution of one minute, these epoch-averagedacceleration values may be advantageously used in the following mannerto detect static body rotational position.

Consistent with the roll detector definition of the rotational positionangle φ, let φ_(T)=a tan 2{Ā_(X,T)(t), Ā_(Z,T)(t)} as before, whereĀ_(X,T)(t) and Ā_(Z,T)(t) are raw (i.e., not high-pass filtered)accelerations averaged over an epoch T. Let β_(T)=the angle of the toesrelative to the vertical. The relation between φ_(T) and β_(T) dependsupon the rotational placement of the TENS device on the upper calf ofthe user, denoted α. Because the electrode gel 444 is sticky and thestrap 110 is supportive, the TENS device does not move on the user's legonce it is placed onto the upper calf 140, therefore the angle α isconstant as long as the TENS device is on the leg of the user.

Looking now at FIG. 9, the double-primed coordinate system (i.e., x″,y″, z″, with y″ not being seen in FIG. 9 since it extends down the axisof the leg) is fixed to the Earth with gravity along the vertical, thesingle-primed coordinate system (i.e., x′, y′, z′, with y′ not beingseen in FIG. 9 since it extends down the axis of the leg) is fixed tothe leg, and the unprimed coordinate system (i.e., x, y, z, with y notbeing seen in FIG. 9 since it extends down the axis of the leg) is fixedto the TENS device measuring Ā_(X,T)(t) and Ā_(Z,T)(t). The Earthcoordinate system has its z″-axis along the vertical, the leg coordinatesystem has its z′-axis in the direction of the toes, and the legrotational angle β is the angle between the Earth x″-axis and legx′-axis. The TENS device angle α is the location of the TENS device onthe leg measured from the leg x′-axis. Using knowledge of theaccelerometer axes in the TENS device, and standard techniques ofgeometry including the identification of similar triangles, it will beevident to those skill in the art that these angles are related simplyby β=180−α−φ. In each epoch, therefore, these angles are related simplyby β_(T)=180−α−φ_(T).

In a preferred embodiment, the following simple procedure is used byprocessor 515 of user state (i.e., leg orientation and leg motion)detector 500 to determine whether the user is on-back through anestimation of the angle β.

Step 1. The user places the TENS device on the lower leg of the user andfastens the strap 110 snugly around their upper calf 140, lies recumbentwith the leg nearly horizontal, points their toes vertically upward, andremains still.

Step 2. The user indicates to the TENS device that the aforementionedconditions have been met. This indication may take the form of a seriesof button presses (e.g., with button 106), a series of taps oncompartment 102 detected by the accelerometer 152, or an indication on asmartphone 860 in communication with the TENS device 100.

Step 3: With the toes pointed upright, β≈0, therefore it is trivial toestimate {circumflex over (α)}=180−{circumflex over (φ)} where{circumflex over (φ)} is estimated from accelerometer data acquiredduring the toe-up period. In order to facilitate calculations, put thisdifference in the range −180°<{circumflex over (α)}≦180°, i.e., if{circumflex over (α)}>180° then subtract 360°, but if {circumflex over(α)}≦−180° then add 360°.

Step 4: In every epoch ending at time T, use this value of {circumflexover (α)} to compute β_(T)=180−{circumflex over (α)}−φ_(T). In order tofacilitate comparisons with a threshold, put this difference in therange −180°<β_(T)≦180°, i.e., if β_(T)>180° then subtract 360°, but ifβ_(T)≦−180° then add 360°.

Step 5: Define a range of values for β_(T) that correspond to the userlying or sleeping on their back. In a preferred embodiment, classifyevery epoch for which −80°<β_(T)<80° as “on-back”. This range issymmetrical so the algorithm works for placement on either leg. Avoiding±90° by 10° excludes the values likely to be encountered when a userlies or sleeps on their side. In another preferred embodiment, thethresholds (which would reside at step 930 in FIG. 10) depend upon theleg on which the device is placed. For example, if the device is placedon the left leg, the most likely range of angles while lying on the backis 0°<β_(T)<80°. Alternatively, if the device is placed on the rightleg, the most likely range of angles while lying on the back is−80°<β_(T)<0°.

Step 6: If the user with sleep apnea selects this option for TENS device100, then when the user is determined to be asleep, i.e., recumbent withlow activity, the TENS device notifies the user if they are on theirback for more than some set amount of time, e.g., a few minutes. Thisindication can be in the form of a vibration of the TENS device itself,or an alarm on their smartphone 860, for example.

Step 7: After determining the span(s) of minutes in which the user waslikely to be asleep, i.e., recumbent with low activity, determine thefraction of minutes in which the user was determined to be on theirback. Report this percentage to this user, e.g., with smartphone 860.

Exemplary Operation

In one preferred form of the invention, TENS device 100, including itsuser state (i.e., leg orientation and leg motion) detector 500, itsprocessor 515 and its controller 520, are programmed to operate in themanner shown in the flowchart of FIG. 10.

More particularly, when TENS device 100 is secured to the upper calf 140of the user and turned on, user state (i.e., leg orientation and legmotion) detector 500 collects data from accelerometer 152, real-timeclock 505 and ambient light detector 510, as shown at step 902. Inaddition, on-skin detector 521 confirms that electrode array 120 of TENSdevice 100 is in contact with the user's skin, as shown at step 904 (andhence confirms that TENS device 100 is secured to the upper calf 140 ofthe user).

Processor 515 analyzes data from accelerometer 152, real-time clock 505and ambient light detector 510, as shown at step 906.

Processor 515 determines the user's leg elevation orientation, as shownat step 908, and determines if the user is in bed by comparing elevationangle with a threshold (i.e., “Threshold4”), as shown at step 910.

If processor 515 determines that the user is in bed, processor 515determines the user's leg activity, as shown at step 912.

The user's leg activity is compared against a threshold (i.e.,“Threshold1”), as shown at step 914, and, if the user's leg activity isbelow that threshold, processor 515 determines that the user is in arestful sleep, as shown at step 916.

Processor 515 also compares the user's leg activity (determined at step912) against another threshold (i.e., “Threshold2”), as shown at step918, and, if the user's leg activity is above that threshold, processor515 determines that the user has excessive leg movement, as shown atstep 920.

In addition to the foregoing, processor 515 also determines the user'sleg rotation orientation, as shown at step 922, and compares the changein the angle of the user's leg rotation against another threshold (i.e.,“Threshold3”), as shown at step 924, and, if the change in the angle ofthe user's leg rotation is above that threshold, and if the user's legmovement exceeds a threshold (i.e., “Threshold2”) as shown at step 918,processor 515 determines that a body roll event has occurred, as shownat step 926.

Also, processor 515 looks at the user's leg rotation orientation, asdetermined at step 922, the accelerometer data analysis, as determinedat step 906 and the user's user limb and toe-up indication, asdetermined at step 928, and determines the user's body positionclassification, as shown at step 930. Processor 515 then characterizesthe user's position as “on back”, “on side (left/right)” or “onstomach”, as shown at step 932.

The information derived at steps 916, 920, 926 and 932 is then utilizedby processor 515 to analyze the user's sleep session, as shown at step934. The results of this sleep analysis (as determined at step 934) maythen be displayed (as shown at step 936), used to provide feedback tothe user or the user's caregiver (as shown at step 938) and/or used todirect controller 520 (as shown at step 940) to modulate the stimulationcurrent provided by TENS device 100.

Modifications of the Preferred Embodiments

It will be appreciated that the present invention provides atranscutaneous electrical nerve stimulator with automatic monitoring ofleg activities and leg orientations. Leg orientations include legelevation and leg rotation state, and changes in leg elevation and legrotation states. The TENS stimulator may be pre-programmed to modify itsoperations in response to the detected user leg activities and legpositions during bed time. In addition, leg orientation and legactivities are used to assess sleep quality and sleep position, all areimportant aspects to improve sleep and health. Leg activity patterns canalso be used to diagnose sleep disorders such as periodic leg movementand the TENS stimulator can be used to alleviate excessive leg movementactivities that are disruptive to sleep.

The present invention can also be realized without the nerve stimulationfunctionality. Body movement and position can be monitored andquantified using the present invention without the need of nervestimulation. The monitoring apparatus (device) can also be placed inother body positions like upper arm of either limb.

Furthermore, it should be understood that many additional changes in thedetails, materials, steps and arrangements of parts, which have beenherein described and illustrated in order to explain the nature of thepresent invention, may be made by those skilled in the art while stillremaining within the principles and scopes of the invention.

1.-54. (canceled)
 55. Apparatus for monitoring the sleep patterns of auser, said apparatus comprising: a housing; an application unit forproviding mechanical coupling between said housing and the user's body;a sensing unit disposed within the housing for (i) sensing the user'sbody movement and body orientation to determine whether the user is in asleep state or a wake state, and (ii) analyzing the sleep state of theuser; and a time-tracking unit for tracking time, wherein the time ofthe time-tracking unit modifies operations of the sensing unit. 56.Apparatus according to claim 55 wherein said time-tracking unit is areal-time clock.
 57. Apparatus according to claim 55 wherein when thetime of said time-tracking unit is within a time period, thetime-tracking unit causes the sensing unit to use more stringentcriteria to determine the sleep state of the user.
 58. Apparatusaccording to claim 57 wherein said time period is during daytime. 59.Apparatus according to claim 57 wherein said time period is outside timeintervals previously determined to be in sleep state for said user. 60.Apparatus according to claim 55 wherein when the time of saidtime-tracking unit is within a time period, the time-tracking unitcauses the sensing unit to use more relaxed criteria to determine theawake state of the user.
 61. Apparatus according to claim 60 whereinsaid time period is during daytime.
 62. Apparatus for monitoring thesleep patterns of a user, said apparatus comprising: a housing; anapplication unit for providing mechanical coupling between said housingand the user's body; a sensing unit disposed within the housing for (i)sensing the user's body movement and body orientation to determinewhether the user is in a sleep state or a wake state, and (ii) analyzingthe sleep state of the user; and a light analyzer for monitoring ambientlight conditions, wherein output of the light analyzer modifiesoperations of the sensing unit.
 63. Apparatus according to claim 65wherein when the output of said light analyzer indicates a bright lightcondition, the light analyzer causes the sensing unit to use morestringent criteria to determine the sleep state of the user. 64.Apparatus according to claim 62 wherein when the output of said lightanalyzer indicates a bright light condition, the light analyzer causesthe sensing unit to use more relaxed criteria to determine the awakestate of the user.
 65. Apparatus according to claim 64 wherein saidbright light condition is an average of light conditions when said useris previously determined to be in awake state.
 66. A method formonitoring the sleep patterns of a user, said method comprising of thesteps of: applying a sensing unit to a body of the user; connecting atime-tracking unit to the sensing unit; setting the operating conditionsof the sensing unit based on a time of the time-tracking unit; and usingthe sensing unit to determine the user's body movement and bodyorientation to (i) determine whether the user is in a sleep state or awake state, and (ii) analyze the sleep state of the user.
 67. A methodaccording to claim 66 wherein said time-tracking unit is a real-timeclock.
 68. A method according to claim 66 wherein the time of saidtime-tracking unit includes time periods previously marked as sleepperiod or wake period by the sensing unit for said user.
 69. A methodfor monitoring the sleep patterns of a user, said method comprising ofthe steps of: applying a sensing unit to a body of the user; connectinga light analyzer unit to the sensing unit; setting the operatingconditions of the sensing unit based on output of the light analyzerunit; and using the sensing unit to determine the user's body movementand body orientation to (i) determine whether the user is in a sleepstate or a wake state, and (ii) analyze the sleep state of the user. 70.A method according to claim 69 wherein said light analyzer unitdetermines ambient light condition around said user.
 71. A methodaccording to claim 69 wherein the state of said light analyzer unitincludes a light condition previously marked as a sleep condition or awake condition by the sensing unit for said user.
 72. Apparatus formonitoring the sleep patterns of a user, said apparatus comprising: ahousing; an application unit for providing mechanical coupling betweensaid housing and the user's body; and a sensing unit disposed within thehousing for (i) sensing the user's body movement and body orientation todetermine whether the user is in a sleep state or a wake state, and (ii)analyzing leg movement patterns during the sleep state of the user. 73.Apparatus according to claim 72 further comprising a feedback unit forproviding the user with feedback in response to the analysis of the legmovement patterns of the user.
 74. Apparatus according to claim 72wherein said leg movement include periodic leg movements.
 75. Apparatusaccording to claim 72 wherein said leg movement patterns include timeand frequency of said leg movement.
 76. A method for monitoring thesleep patterns of a user, said method comprising of the steps of:applying a sensing unit to a body of the user; and using the sensingunit to determine the user's body movement and body orientation to (i)determine whether the user is in a sleep state or a wake state, and (ii)analyze leg movement patterns during the sleep state of the user.
 77. Amethod according to claim 76 further comprising providing the user withfeedback via a feedback unit in response to the analysis of the legmovement patterns.
 78. A method according to claim 76 wherein said legmovement include periodic leg movements.
 79. A method according to claim76 wherein said leg movement patterns include time and frequency of saidleg movement.
 80. Apparatus according to claim 73 wherein the feedbackis electrical stimulation.
 81. Apparatus according to claim 73 whereinthe feedback is mechanical vibration.
 82. A method according to claim 77wherein the feedback is electrical stimulation.
 83. A method accordingto claim 77 wherein the feedback is mechanical vibration.